Coupling orthogonal polarizations in a common square waveguide with modes in individual waveguides



Sept. 22, 1964 D F. BowMAN 3,150,333

COUPLING ORTHOGONAL POLARIZTIONS IN A COMMON SQUARE WAVEGUIDE WITH MODES IN INDIVIDUAL WAVEGUIDES J re 0L 'e/ve, 515E@ @1 -26 fof/ce Sept. 22, 1964 D. F. BowMAN 3,150,333

couPLING oRTHoGoNAD PoLARIzAIIoNs IN A COMMON SQUARE wAvEGuIDE WITH MoDEs IN INDIVIDUAL wAvEGuIDEs Filed Feb. 1, 1960 5 Sheets-Sheet 2 N N N I y lll' eaz. EAM, F4556, 61E/e5 g Sar/ffm Sept. 22, 1964 WMAN 3,150,333

D F. BO COUPLING ORTHOGONAL POLARIZATIONS IN A COMMON SQUARE WAVEGUIDE WITH MODES IN INDIVIDUAL. WAVEGUIDES Filed Feb. l, 1960 3 Sheets-Sheet 5 N I w 31 I`| S e v ,5 o 00N E INVENTOR.

O ryaeaL EN@ Passe, Giles g {bf/EN United States Patent O 3,150,333 COUPLING ORTHOGONAL POLARIZATIONS IN A COMMON SQUARE WAVEGUIDE WITH MODES IN INDIVIDUAL WAVEGUIDES David F. Bowman, Wayne, Pa., assignor, by mesne assignments, to Airtron Division of Litton Pre- `cision Products, Inc., Morris Plains, NJ., a corporation of Delaware Filed Feb. 1, 1960, Ser. No. 6,036 3 Claims. (Cl. S33- 9) My invention relates generally to broad-band, dual polarization, microwave apparatus, and more particularly relates to novel microwave horns that combine two independent signal bands polarized in 90 space Irelationship with substantially constant impedance characteristics.

In accordance with my present invention, two waveguides for independent microwave bands terminate in individual T waveguide sections that lare physically intercoupled. The intercoupled T sections have mutually perpendicular openings. The lbranch openings of the T sections are joined With the novel horn hereof, along its throat region. A generally pyramidal core extends centrally of the horn, tapered from its throat to the aperture, effecting a continuous wave front of the two signals.

My invention app-aratus is particularly applicable in the 300 to 3,000 megacycle region. The composite horn system hereof is typically useful to illuminate a lens, or as a feed horn for a parabolcidal reflector antenna. The system is bidirectional, and can be used to pick-up dual polarized signals for separation and transmission to separate waveguides. Further, in some instances, the horn aperture may be coupled to a well balanced waveguide for composite transmission of two signal bands from two waveguides.

An important feature of my invention system is the very low input retlection coetiicient resultant in operation over wide signal bands. The horn smoothly translates the dual bands with substantially constant or slowly varying characteristic impedance maintained along its structure. Also, it is capable of handling high power levels, eg., 100 kilowatts of average power at the indicated frequency range, not far reduced from the inherent power level capacity of the input waveguide. This is due to the complete absence of serious constrictions within the wave passage cross-section. The horn system described hereinafter is used with the two original signals being impressed upon the horn and radiated therefrom, as to a reflector. Other uses are of course contemplated.

In the exemplary system, two E-plane Ts are used, each with two symmetrical half-height waveguide branches. The waves from the two inputs share a common passage starting at the throat of the horn. At this point, the waves are still quite distinctly separated, but as they progress along the length of the horn toward the aperture they gradually become less so. At the aperture, they mutually occupy the entire cross-sectional area of the horn. The taper of cross-sectional area in the horn is accomplished by a pyramidal core. The phasing of the branch guides is such that the waves from opposite guides join at the aperture to form a continuous wave front.

The perfect symmetry provided in each waveguide hereof, from the E-plane Ts Iforward to the aperture of the horn, is of significant advantage. High order waveguide modes having even .symmetry that otherwise might be excited, are completely avoided. It is accord- 3,150,333 Patented Sept. 22, 1964 lCe ingly unnecessary to provide straight lengths of guide for mode filtering. High order even symmetry modes, if excited, have a deleterious efect on the symmetry of the horn pattern, and have a bandwidth narrowing effect if they are cut-olf at a location away from the point where they are excited.

There are negligible impedance reflections in the invention system, for either band transmission or reception. A good input standing-wave rat-io over the wide bands prevails, 'being of the order of 1.05 and better. This feature overcomes an important defect of the prior art constructions. The horn hereof employs novel smooth impedance transformation therein. The core or interior pyramid is Iproportioned to control and minimize the VSWR for the desired horn shape. Nowhere in the horn or T sections herein need the cross-section be restricted.

The horn Iof .the present invention is inherently broadband. However, for ycritical performance requirements, impedance tuning controls may Ibe readily incorporated. Such controls could be in the form of adjustable inductive posts or tuning screws. Such normally would require only a small range of adjustment. The arrangement of the wave passages within the horn hereof allows substantial freedom in applying tuning control-s to the wave of one polar-iztaion, without affecting the wave of the other polarization.

It is accordingly an important object of my present invention to provide a novel horn for .combining two waves polarized apart.

Another object of my present invention is to provide a novel horn system including two interrelated T sections in 90 rela-tion for dual polarized waves.

A further object of my present invention is to provide a novel microwave system for smoothly combining (or separating) two signal bands polarized 90 apart, with low input standing-wave ratios.

Still another .object of my present invention is to provide a novel microwave system for two Wave bands, with separate T sections having branches nested together.

Still a further object of my present invention is to provide a novel horn with two independent signal inputs at 90 relation, having a core that smoothly `combines these inputs into a continuous wave front.

Still `a further object of my present invention is to provide a novel horn with two independent waveguide signal inputs leading to wave passages free of constrictions and obstructions that would lower their power handling capability.

These 4.and `further objects of the invention will become evident from the following description of an exemplary embodiment .thereof illustrated in the drawings, in which:

FIGURE 1 is a side elevational horn with twn T input.

FIGURES 2 through 5 a-re diagrammatic representations used in the exposition of the T sections hereof.

FIGURE 6 is a cross-sectional view through the horn taken along the line 6-6 .of FIGURE 1.

FIGURE 7 is a partly sectional view of the nested twin T sections taken along the line 7 7 in FIGURE 1, in the direction of the arrows.

FIGURE 8 is a perspective view of the exemplary horn assembly, with the horn in-terior exposed.

FIGURES 9 and 10 are perspective views ofthe respective T sections of the input of horn of FIGURES 1 and 8.

FIGURES 11, 12 and 13 are diagrams used in describing the operation of the horn.

FIGURES 14 and 15 are modified horn systems.

FIGURE 16 is an end view of the horn of FIGURE 15, looking to the right.

FIGURES l and 8 illustrate the exemplary twin-T horn assembly composed of horn unit 25 and a nested T section 30 coupled therewith. The horn assembly 20 may be used to provide a high-power, broadband, dual polarization feed at aperture 21 for paraboloidal reliector antennae. The system 20 may be used inversely, to pickup a dual polarized wave front as c at its aperture 21 and separate it into independent Waves a and b polarized 90 apart. As a feed system, two signals A, B in the band of operation are impressed, as through waveguides indicated in dotted lines at 31, 32, respectively to the inputs 33, 34 or twin-T sections 35, 40. The output wave C at aperture 21 would then be a continuous wavefront, with dual polarization at 90 of waves A and B.

The twin-T sections 35, 40 are nested as an assembly 30. Each T-section is an E-plane T section arrangement with two branches: FIGURE 2 illustrates in cross-section a conventional T at 50 with trunk 51 and branches 52, 53. The center-line 54 may be viewed as electrically dividing the T 50 into two individual right angle bends. FIGURE 3 illustrates in cross-section such bends 55, 56 corresponding to those of FIGURE 2. In FIGURE 4, the corresponding bend sections 55', 56', shown in crosssection, are provided with mitered corners 57, 58 (which may be rounded) to reduce reflections for smooth wave passage about the 90 bends.

By joining bend sections 55', 56 along the line of symmetry, the T section 60 of FIGURE 5 results, shown in cross-section, with central trunk 61 and right angled portions 62, 63. The miters 64, 65 correspond to 57, 58 of FIGURE 4. The T section 60 diagrammatically represents the double or twin Ts 35, 40 of the invention. These Ts are arranged as E-plane inputs, as at trunk 61 for input wave w, signals arrows s, s indicating the polarity of a travelling wave in the TEM) mode. The lirst set of bends 62, 63 are at right angles, and each of halfheight in their E-plane as indicated. The s wave splits into two equal parts along bends 62, 63; as corresponding half power wave s', s having the same power density as wave s.

The T 60 is provided with a further 90 bend at the end of each branch 62, 63. Branch 62 is joined with bend section 66 parallel to trunk 61; and branch 63, with bend section 67 parallel to section 66. Corner miters 68 and 69 smooth the wave bending for emergent waves S", S". It is thus noted that original wave w emerges as two corresponding Waves w', w each one-half of the power of input wave w. The progress of signal s in the T 60 branches is as shown by the arrows` in FIGURE 5, and emerges as two spaced equal waves w', w', each of half strength, but together equal to the input energy of wave w.

Referring now to FIGURES 6 and 7, it is seen that the original input wave A at 33 (FIGURE l) becomes two spaced TEN mode waves A', A at branch outputs 70, 71 of T 35, in the manner described hereinabove in connection with FIGURE 5. In a similar manner, wave B at input 34, of T 40 (FIGURE 1) emerges at the two branches, through outputs 72, 73, as two spaced waves B', B' in the E-plane of wave B. It is to be noted that the space orientation of the waves A and B at openings 70, 71, 72, 73 are at 90. Further, branch openings 70, 71, 72, 73 are arranged as adjacent peripheral pairs along the throat region 26 of horn 25.

A core 75 extends from the throat 26 region of horn 25, tapered axially towards the horn aperture 27. FIG- URE 8 shows the exemplary pyramidal core 75 in perspective. Each side 76 of core 75 is flat and extends from the interior edge of its associated T branch opening 70, 71, 72, 73. The triangular sides 76, 76 taper to the pyramid apex 77. Each pyramid side 76, 76 together With the corresponding side wall 78, 78 of the horn 25 forms an E-plane taper. The effective taper of the waveguide may be controlled by proper proportioning of the core with respect to the surrounding walls. Such tapers in the horn provide a gradual transition from each of the half-height branch guides to one-half of the aperture 21. The waves A', A and B', B from the opposite guide T s 35, 40 are thereby joined at the aperture 21 region of the horn to form a continuous composite wave front C. Corner plates 79, 79 prevent leakage from the basically rectangular or square shaped horn 25. If desirable, the transition from the half height guides to the aperture may be made electrically more gradual. Thus, the addition of corner fillets in the manner of patent application Serial No. 5,299, tiled January 28, 1960, now Patent No. 3,026,- 451, entitled Dual Polarized Horn, inventor Cyril Carson, and assigned to the assignee of the instant application, and/ or arrays of conducting rods, would accomplish such result.

The nested T section 30 is proportioned to provide paired branch openings 70 to 73 that physically join with the throat region 26 of horn 25, about the base of core '75. The waveguide passage of the interior T section 40 is illustrated in perspective in FIGURE 9; and that of overlap T section 35, in FIGURE 10.

It is noted that the E-plane configuration of waveguide section 35 `corresponds to that described for T unit 60 of FIGURE 5. The input or trunk portion 36 has a normal E-plane width of 4.875 in the exemplary apparatus, with a corresponding H-plane dimension of 9.750. This coniiguration is practical in using the wide band of 755 to 955 megacycles in the system. For other frequencies or band width correspondingly different dimensions are contemplated.

The first bends 37, 37 extend 90 to trunk 36, and thereupon further bends for branches 38, 38. The bends are separated by approximately wave length at the mean frequency, and suitably smoothed by rounded edges or miters. The basic input wave A at 36 produces two branch Waves A', A of half-power at branches 38, 38, and out through branch openings 70, 71 (see also FIGURES 6 and 7).

The interior T section 40 has its E-plane arranged perpendicular to that of T section 35. The input trunk is composed of two portions 41, 42 at a 90 bend. Both trunk portions 41, 42 are of full E-plane width. The remainder of T section 40 from portion 41 on to the branch openings 72, 73 is arranged in principle to that of T sections 35 and 60 (FIGURE 5). The purpose of added initial bend 41 is to introduce the B wave into section 40, otherwise nested internally of T section 35.

The T section 40 is composed of initial trunk bend 41, 42, and two 90 half-Width arms 43, 43 that lead to end branch arms 44, 44. The respective branch openings 72, '73 are at the end of arms 44, 44. The basic input wave B at 41 produces two branch waves B, B at half-power in branches 44, 44, and out through branch openings 72, 73 (see also FIGURES 6 and 7).

The cavity or opening 39 formed between the branches 38, 38 is made just suiiicient for the basic assembly of T waveguide 40 to nest within. The extending dotted lines 45, 45 from units 35, 40 of FIGURES 9 and l0 indicate the coacting dimensions for the nesting, wherein branches 38, 38 extend over unit 40, with trunk portion 41 of unit 40 juxtaposed with bend sections 37, 37 of unit 35. It is understood that trunk section 41 extends exterior of nesting region 39, and supports the input flange 34 (see FIG- URE 8). Also, the wall thickness for the waveguide passages are accounted for. There is no critical dimensioning involved therein. The corner mitering is not shown in FIGURE 8.

The discontinuity due to a bend in each branch guide would correspond to a l1 of .025 if uncompensated, where I' is the magnitude of the retiection coetiicient. It is noted that mitering is indicated at the bends of T sections 35, 40. With suitable mitering, l1 can ready be reduced to 01 maximum over the bend. The corresponding half of the E-plane T is preferably given exactly the same configuration as the bend, and will thus have the same reflection coefficient. The electrical spacing between these two reflections is 90 at midband. This results in full cancellation at midband, and cancellation to I=.O006 at edgeband. The mitered bend in the side input 41 is matched as a separate operation.

Matched T guides are thus provided for the two polarizations up to the throat 26 of the horn 25. The proportioning of the core 75 in the dual-polarization horn further smoothly transforms the impedance and passage of the two waves A and B therethrough, to free space at the horn aperture. The length and rate of taper of the pyramidal core 75 is selected to smoothly alter the impedance and guide wavelength for this portion of the apparatus.

FIGURE ll illustrates diagrammatically the core 75 in horn 25, with the pyramid sides 76, 76 coacting to form an impedance transformation means with horn sides 78, 78 between input branch openings 70, 71 and aperture 27. The exemplary horn is square in crosssection, and the E-plane widths of T sections 35, 40 are equal. The system hereof is of course equally applicable to rectangular horn configurations with differing T input dimensions, and also conical forms (see FIGURES 14 through 16).

FIGURES 12 and 13 are cross-sectional field diagrams along pyramid 75 (FIGURE 1l) showing square pyramid sections. The waves A, A, at position 13-13 of FIGURE ll (FIGURE 13) are seen to still be between the pyramid sides 76, 76 and the horn sides 78, 78. Further out, at position 12-12 (FIGURE 12), some lines of force of waves A" extend between opposite horn walls 78, 78, having disengaged from the core 75. At the aperture 27 and core apex 77, full disengagement, in a smooth transition, occurs. Similarly, in the 90 position of wave B across wave A, a transition to corresponding waves B and B" (not shown) occurs, merging as a continuous dual-polarized wave C at the horn aperture.

The pyramid configuration also is a factor in the effective polar radiation pattern resultant from the horn, in conjunction with the horn shape. The sides of the horn may be parallel as shown in the exemplary form 25, or may be inclined to either increase or decrease the aperture area. Also, the horn hereof may be cylindrical or conical in shape. In FIGURE 14, the horn 80 is a truncated cone, with sides tapered to result in a reduced area aperture 81 over that of the throat 82 area. The central core 83 is conical to effect the smooth impedance transformation required, and wave integration. The apex 84 of cone 83 may be interior of horn 80 as shown, or at the aperture 811. The horn impedance twin-T unit 8S is similar to unit hereinabove, with two separate signal input guides 86, 87. In this case, however, the branch openings from twin-T unit 85 are accurate as described in connection with FIGURE 16 hereinafter.

FIGURE l5 illustrates a further form for the horn, at 90. Horn 90 is a truncated cone with its horn aperture 91 larger than the throat region 92. The conical core 93 extends close to aperture 91 with its apex 94. The twin-T unit 95 is composed of two nesting branch Ts 96, 97. As seen in end view, FIGURE 16, the branch openings 98, 98 for T guide 97 are arcuate at the throat region 92. The input trunk portions of the T guides 96, 97 may be circular, square or rectangular. Also the horn 90 may contain a flare.

The shape of the horn is basically determined by the desired frequency range and polar pattern of radiation in accordance with well known horn theory. The core is coordinated with the desired horn configuration for smooth impedance transformation and wave combination therein. The horn aperture may be made to radiate into a reflector or lens, or into free space, and is constructed accordingly. While the exemplary apparatus has been described for transmitter use, it is understood that it may be operated in receiving apparatus in the inverse mode referred to hereinabove.

While the exemplary apparatus uses twin-T sections 35, 40 with 90 bends, it is to be understood that other configurations may instead be employed within the scope of this invention.

Generally, a Y-junction may be used, with any requisite angle, in place of the or 180 arrangement of the T arms in sections 35, 40 of the illustrative system 20. The particular T section, or equivalent structure, is selected for advantages in matching, in a given system. Their interrelation and 90 spatial feeding about the throat of a horn, with an impedance matching core is the significant aspect hereof. Also the core 75 may be stepped and/or tapered as will now be understood by those skilled in the art.

Although the invention has been described in connection with exemplary embodiments thereof, it is to be understood that variations and modifications may be made within the broader spirit and scope of the invention, as set forth in the following claims.

I claim:

1. A signal coupler comprising a horn with a first end opening and a second end opening opposite thereto, wall areas joining said openings, and a central pyramidal core within said horn coactable with said wall areas for smoothly transforming the impedance between said openings, the base of said core being positioned at said first opening, the sides of said core extending substantially the entire distance between said first and second openings, and coacting with said wall areas to define a plurality of pairs of wave passages substantially 90 apart for first and second independent wave signals, first and second guide means for coupling said first and second independent wave signals to said first opening about the base of said core; each of said guide means including a pair of openings for coupling into their respective pair of said wave passages, with the wave energy therein being propagated substantially parallel to the longitudinal axis of said horn, the pair of openings of said first signal coupler respectively located intermediate Opposed first and third base edge surfaces of said pyramidal core and the adjacent inner wall surfaces of said horn; the pair of openings of said second signal coupler respectively located intermediate opposed second and fourth base edge surfaces of said pyramidal core and the adjacent inner wall surfaces of said horn, said second and fourth base edge surfaces perpendicular to said first and third base edge surfaces and extending therebetween to define a square enclosed area wherein the base of said pyramidal core is contained, said passages merging towards the apex of said pyramidal core, whereby the two wave signals are combined at the core apex located at the second opening.

2. A signal coupler as claimed in claim 1, said first guide means including la first T waveguide coupled to one of said pairs of wave passages with two spaced guide branches, said second guide means including a second T waveguide coupled to the other of said pairs of wave passages with two spaced guide branches, said second waveguide being contained between the spaced guide branches of said first waveguide in nested arrangement therewith.

3. A signal coupler as claimed in claim 1, said first guide means including a first T waveguide coupled to one of said pairs of wave passages with two parallel spaced guide branches having half-width E-plane dimensions in the direction between the core and wall areas, said second guide means including a second T waveguide coupled to the other of said pairs of wave passages with two parallel spaced guide branches having half-width E- plane dimensions in the direction between the core and wall areas, said second waveguide being contained within the spaced guide branches of said first waveguide in nested arrangement therewith the E-planes of the respective branches of said waveguides being oriented at :substantially 90 `to each other and the sides of the core References Cited in the le of this patent UNITED STATES PATENTS Roberts Nov. 19, 1946 Braden Oct. 31, 1950 Raabe May 20, 1958 Honey et al Sept. 27, 1960 Lewis Dec. 20, 1960 Ohm a June 19, 1962 OTHER REFERENCES Honey: A Versatile Multiport Biconical Antenna, Proceedings of the IRE, vol. 45, No. 10, October 1957, pages l3741383. 

1. A SIGNAL COUPLER COMPRISING A HORN WITH A FIRST END OPENING AND A SECOND END OPENING OPPOSITE THERETO, WALL AREAS JOINING SAID OPENINGS, AND A CENTRAL PYRAMIDAL CORE WITHIN SAID HORN COACTABLE WITH SAID WALL AREAS FOR SMOOTHLY TRANSFORMING THE IMPEDANCE BETWEEN SAID OPENINGS, THE BASE OF SAID CORE BEING POSITIONED AT SAID FIRST OPENING, THE SIDES OF SAID CORE EXTENDING SUBSTANTIALLY THE ENTIRE DISTANCE BETWEEN SAID FIRST AND SECOND OPENINGS, AND COACTING WITH SAID WALL AREAS TO DEFINE A PLURALITY OF PAIRS OF WAVE PASSAGES SUBSTANTIALLY 90* APART FOR FIRST AND SECOND INDEPENDENT WAVE SIGNALS, FIRST AND SECOND GUIDE MEANS FOR COUPLING SAID FIRST AND SECOND INDEPENDENT WAVE SIGNALS TO SAID FIRST OPENING ABOUT THE BASE OF SAID CORE; EACH OF SAID GUIDE MEANS INCLUDING A PAIR OF OPENINGS FOR COUPLING INTO THEIR RESPECTIVE PAIR OF SAID WAVE PASSAGES, WITH THE WAVE ENERGY THEREIN BEING PROPAGATED SUBSTANTIALLY PARALLEL TO THE LONGITUDINAL AXIS OF SAID HORN, THE PAIR OF OPENINGS OF SAID FIRST SIGNAL COUPLER RESPECTIVELY LOCATED INTERMEDIATE OPPOSED FIRST AND THIRD BASE EDGE SURFACES OF SAID PYRAMIDAL CORE AND THE ADJACENT INNER WALL SURFACES OF SAID HORN; THE PAIR OF OPENINGS OF SAID SECOND SIGNAL COUPLER RESPECTIVELY LOCATED INTERMEDIATE OPPOSED SECOND AND FOURTH BASE EDGE SURFACES OF SAID PYRAMIDAL CORE AND THE ADJACENT INNER WALL SURFACES OF SAID HORN, SAID SECOND AND FOURTH BASE EDGE SURFACES PERPENDICULAR TO SAID FIRST AND THIRD BASE EDGE SURFACES AND EXTENDING THEREBETWEEN TO DEFINE A SQUARE ENCLOSED AREA WHEREIN THE BASE OF SAID PYRAMIDAL CORE IS CONTAINED, SAID PASSAGES MERGING TOWARDS THE APEX OF SAID PYRAMIDAL CORE, WHEREBY THE TWO WAVE SIGNALS ARE COMBINED AT THE CORE APEX LOCATED AT THE SECOND OPENING. 